Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles
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💡 Waking up between sleep cycles means you'll feel more refreshed. The highlighted times give you the most complete cycles.
About Sleep Cycles
What is a sleep cycle?
Sleep occurs in 90-minute cycles, each containing light sleep, deep sleep, and REM (rapid eye movement) sleep. Waking up at the end of a complete cycle — rather than in the middle of one — makes you feel much more rested and alert.
How many cycles do I need?
Most adults need 5–6 complete cycles (7.5–9 hours). Teenagers and children need more. The 6-cycle (9-hour) option is ideal if you can manage it; 5 cycles (7.5 hours) is the practical sweet spot for most adults.
What about REM sleep?
REM sleep is critical for memory consolidation, learning, and emotional regulation. REM cycles get longer later in the night, so cutting sleep short — even by 90 minutes — significantly reduces total REM sleep.